Water-swelling elastic plugging agent for water-based drilling fluid and preparation method thereof

Abstract

The invention discloses a water-swelling elastic plugging agent for a water-based drilling fluid and a preparation method of the water-swelling elastic plugging agent. The water-swelling elastic plugging agent comprises the following components in parts by weight: 100 parts of a polyolefin elastomer matrix material; 15 to 20 parts of a reinforced matrix material; 0.8 to 1.5 parts of a polyolefin elastomer matrix material cross-linking agent; 8 parts to 15 parts of a reinforcing agent A; 20 to 30 parts of a reinforcing agent B; 15 to 30 parts of super absorbent resin; 15 to 20 parts of a plasticizer; 0.2 to 0.8 part of an isolating agent; 0.5 to 1 part of an anti-aging agent; the plugging agent provided by the invention is simple in preparation process, not only is beneficial to industrial production, but also is convenient to prepare plugging slurry on site, can achieve a good plugging effect, and provides an effective technical means for well leakage treatment.

Description

Technical Field

[0001] This invention relates to the field of oil and gas drilling leakage control and plugging technology, and in particular to a water-based drilling fluid water-absorbing and expanding elastic plugging agent and its preparation method. Background Technology

[0002] The geological structure in the Sichuan-Chongqing region is extremely complex, posing a significant challenge to drilling operations. Due to geological features such as fractures, pores, and karst caves, drilling fluid may leak into the formation, causing a drop in wellbore pressure and impacting drilling safety and efficiency. Well leakage not only prolongs drilling time and increases costs but can also lead to serious issues like wellbore collapse and formation instability. Furthermore, well leakage poses a potential risk of groundwater pollution, causing adverse environmental impacts.

[0003] Currently used plugging materials have poor or almost no deformation capacity during plugging. Their size and shape do not match the pores and fractures of the leaking formation, making it difficult for them to penetrate the formation. They can only accumulate on the surface, forming a "sealing" phenomenon. Conventional plugging materials lack sufficient pressure resistance and cannot effectively seal formation fractures and pores. Plugging materials with some deformation capacity, such as cement slurry or gel-based plugging agents, have difficulty controlling their setting time or are rapidly diluted downhole. Under high temperature and pressure, they leak before reaching the ideal curing strength, failing to form a complete solidified body. High filtration loss and cement slurry plugging still have shortcomings in terms of construction safety and pollution resistance. Existing elastic plugging agents, such as polymer gels, need improvement in temperature resistance and pressure resistance. When dealing with well leakage in complex formations such as simultaneous blowouts and multi-pressure systems, they suffer from problems such as multiple plugging attempts and low success rates. Polyolefin elastomer plugging agents lack expansion properties and easily slip after entering the leaking formation, failing to provide good support and sealing.

[0004] Therefore, a water-absorbing, swellable, elastic plugging agent for water-based drilling fluids was invented to meet current drilling fluid plugging needs. A literature search revealed no relevant research on water-absorbing, swellable, elastic plugging agents for water-based drilling fluids; this type of plugging agent is currently in a research gap.

[0005] Patent application CN117431040A discloses a gel slug plug for oil-based drilling fluids and its application, comprising: 30-60 parts by weight of a thermoplastic oleophilic polymer, 30-60 parts by weight of rigid particles, and 10-30 parts by weight of flexible fibers, etc.; the thermoplastic oleophilic polymer is a mixture of amorphous oleophilic materials, crystalline oleophilic materials, and reinforcing agents. After the oleophilic polymer in the gel slug plug for oil-based drilling fluids provided by this invention is pumped into the lost circulation zone, it can form a slug with strong viscosity under the action of formation temperature and oil-based drilling fluid. The compounded rigid particles and flexible fibers can seal formation pores and fractures on the one hand, and synergistically improve the pressure-bearing capacity of the gel slug on the other hand, together with the oleophilic polymer. The formed slug plug can effectively seal the lost circulation zone of oil-based drilling fluid and isolate the oil-based drilling fluid from the formation fluid, thereby achieving effective sealing of the formation where leakage and formation coexist. This invention also provides a method for preparing the gel slug plug for oil-based drilling fluids.

[0006] However, the plugging agent in this patent is for oil-based drilling fluids and cannot be used for plugging water-based drilling fluids. The plugging agent prepared by this patent is formed by physical mixing, which may have problems such as uneven composition, performance fluctuation, poor long-term stability, and poor functional synergy. In addition, this patent uses traditional polymer material processing equipment, and granulation is required after mixing, which is time-consuming and inefficient. Summary of the Invention

[0007] The present invention aims to provide a water-based drilling fluid water-absorbing and expanding elastic plugging agent and its preparation method. The preparation process of the plugging agent is simple, which is conducive to industrial production and easy to prepare plugging slurry on site. It can also achieve good plugging effect and provide an effective technical means for well leakage treatment.

[0008] To achieve the above-mentioned objectives, the technical solution of the present invention is as follows: A water-based drilling fluid water-absorbing and swelling elastic plugging agent comprises the following components in parts by weight: Polyolefin elastomer matrix material: 100 parts; Reinforced matrix material: 15-20 parts; Crosslinking agent for polyolefin elastomer matrix materials: 0.8 parts to 1.5 parts; Enhancer A: 8-15 parts; Enhancer B: 20-30 parts; Superabsorbent polymer: 15-30 parts; Plasticizer: 15-20 parts; Separating agent: 0.2 parts to 0.8 parts; Anti-aging agent: 0.5 parts to 1 part; The superabsorbent resin is prepared by the following steps: S1. Add the water-absorbing monomer, water-locking monomer and initiator to distilled water in sequence, stir at room temperature until completely dissolved, and remove oxygen by bubbling with inert gas to obtain the reaction monomer solution. S2. The monomer solution in step S1 is stirred and reacted under anaerobic conditions for 4-8 hours at a reaction temperature of 40℃-70℃. After the reaction, the water is dried and the solution is ground to obtain a superabsorbent resin. The water-absorbing monomer is one or more of sodium acrylate, sodium methacrylate, acrylamide, and methacrylamide; The water-locking monomer is one or more of sodium 2-acrylamide-2-methylpropanesulfonate, sodium p-styrenesulfonate, sodium propylenesulfonate, and sodium methpropylenesulfonate. The initiator is a commonly used free radical initiator, such as ammonium persulfate, potassium persulfate, etc. The mass ratio of the water-absorbing monomer, the water-locking monomer, and the initiator is 0.2-0.3:0.7-0.8:0.005-0.01.

[0009] The total concentration of the reactant monomer solution is 200 g / L to 300 g / L.

[0010] The polyolefin elastomer matrix material is styrene-butadiene-styrene block copolymer (SBS).

[0011] The reinforcing matrix material is one or more of polypropylene, polystyrene, and polycarbonate.

[0012] The reinforcing agent A is one or more of silica, carbon black, and calcium carbonate, and the particle size of reinforcing agent A is 25μm-50μm.

[0013] The reinforcing agent B is a carbon nanotube (the surface can be hydroxyl, amino, carboxyl, epoxy, mercapto, etc.), the length of the carbon nanotube is 20μm-25μm, and the aspect ratio of the carbon nanotube is 800:1-1000:1.

[0014] The plasticizer is one or more of paraffin oil, aromatic oil, and naphthenic oil.

[0015] The separating agent is one or more of zinc stearate, polyvinyl alcohol, and paraffin.

[0016] The antioxidant is a phenolic antioxidant, such as antioxidant 1010 and antioxidant 264.

[0017] The crosslinking agent for the polyolefin elastomer matrix material is a peroxide crosslinking agent (dicumyl peroxide DCP, di-tert-butyl peroxide DTBP, 2,5-dimethyl-2,5-di-tert-butyl peroxide DBPH, benzoyl peroxide BPO, dodecyl peroxide, etc.).

[0018] A method for preparing a water-based drilling fluid water-absorbing and swelling elastic plugging agent includes the following steps: S11. Add the polyolefin elastomer matrix material and the reinforcing matrix material to a high-speed mixer and stir at a speed of 1300 r / min to 1400 r / min, a temperature of 180℃ to 190℃, and a time of 2 min to 3 min. S12. After stirring, add the polyolefin elastomer matrix material crosslinking agent, reinforcing agent A, reinforcing agent B, superabsorbent resin, plasticizer, release agent and antioxidant in sequence. Stir at high speed, with a speed of 1300 r / min to 1400 r / min, a temperature of 180℃ to 190℃, and a time of 12 min to 15 min. S13. After mixing, the particles with a particle size of 10 to 40 mesh are screened out, which is the water-based drilling fluid water-absorbing and expanding elastic plugging agent.

[0019] The beneficial effects of this invention are: 1. The water-based drilling fluid plugging agent of this invention can enter micro-channels under its own elasticity, with a rebound rate of over 30%, thereby increasing the elasticity of the entire sealing layer and achieving the effect of "entering and stopping," thus improving the success rate of plugging. The drilling fluid plugging agent of this invention exhibits unique performance during the plugging process. Its ability to enter micro-channels is due to its excellent flexibility and deformability. When the plugging agent comes into contact with the wellbore, under pressure, the polymer material in this invention rotates within its single bonds, undergoing elastic deformation, allowing it to adapt to micro-channels of different shapes and sizes, thus smoothly entering them. The high rebound rate is due to the elastic memory effect of the polymer material in this invention. After entering the channel, the plugging agent is compressed by the surrounding environment, but the polymer chains do not undergo permanent deformation. Once the pressure decreases or is eliminated, the polymer chains, relying on their inherent elastic recovery force, attempt to return to their original state, thus exhibiting a high rebound rate. This property allows the plugging agent to adhere closely to the orifice wall, providing an effective sealing effect, while maintaining good sealing stability under pressure changes.

[0020] 2. The water-based drilling fluid water-absorbing and swelling elastic plugging agent of this invention has a pressure resistance of not less than 5.0 MPa, far exceeding that of gel-based polymeric elastic plugging agents. Firstly, the polymeric materials in this invention typically have long-chain molecular structures, and these chains can form a cross-linked network through physical or chemical interactions. When the plugging agent enters the lost formation, the cross-linked network deforms under pressure, but due to intermolecular forces, it effectively resists further deformation. This cross-linked structure endows the plugging agent with high strength and toughness, enabling it to withstand greater pressure. Secondly, the polymeric materials in this invention have a relatively high elastic modulus, which can resist external pressure to a certain extent without significant deformation. When the plugging agent comes into contact with the formation, it can tightly adhere to the walls of the lost channel, forming an effective seal. Simultaneously, the viscoelasticity of the polymeric material also allows it to deform to a certain extent under pressure, thereby dispersing pressure and improving the overall pressure resistance.

[0021] 3. The water-based drilling fluid water-absorbing and swelling elastic plugging agent of this invention has a temperature resistance of up to 160℃. The polymer material in this invention has a stable chemical structure. Its molecular chains are not easily broken or decomposed under high-temperature environments. The polymer material in this invention contains heat-resistant functional groups and cross-linked structures, enabling it to maintain the stability of its physical and chemical properties at high temperatures. When used as a plugging agent, it can effectively seal even in high-temperature drilling environments. Simultaneously, the thermal stability of the polymer material in this invention prevents the plugging agent from excessively softening and deforming at high temperatures. It can maintain a certain strength and hardness, continuing to seal leakage channels. Moreover, the plugging agent in this invention can interact with other components in the drilling fluid to form a more stable structure, enhancing its temperature resistance. For example, it can synergistically work with some temperature-resistant additives to improve overall heat resistance, ensuring that drilling fluid leakage can still be effectively prevented under high-temperature conditions.

[0022] 4. The water-based drilling fluid water-absorbing and swelling elastic plugging agent of this invention has a water absorption volume expansion rate greater than 90%, indicating that the plugging agent can fully expand and seal formation fractures and pores in the leakage layer. The water-absorbing resin in this invention is a functional polymer material with high water absorption. When it comes into contact with water, the hydrophilic groups in the water-absorbing resin quickly combine with water molecules. These hydrophilic groups can adsorb and fix a large number of water molecules in their structure through hydrogen bonds, ionic bonds, and other forces. The polymer material in this invention itself has a certain degree of flexibility and elasticity, which can provide support and containment space for the water-absorbing resin. As the water-absorbing resin continuously absorbs water, its volume expands rapidly, and the polymer material also deforms accordingly, thus significantly increasing the overall volume of the plugging agent. Furthermore, there is a certain interaction between the polymer material and the water-absorbing resin in this invention, further promoting the water absorption process. This synergistic effect allows the plugging agent to absorb a large amount of water in a short time and produce significant volume expansion, effectively sealing the leakage channels of the drilling fluid.

[0023] 5. The preparation process of the water-based drilling fluid water-absorbing and swelling elastic plugging agent of the present invention is simple, requiring only a high-speed mixer, without the use of complex equipment (such as extruders, injection molding machines, open mills, internal mixers, etc.) used in traditional polyolefin processing, and is suitable for industrial mass production. Attached Figure Description

[0024] Figure 1 This is a schematic diagram showing the relationship between volume expansion rate and time in the volume expansion rate test of the water-based drilling fluid water-absorbing and expanding elastic plugging agent of the present invention.

[0025] Figure 2 This is a product image of the water-based drilling fluid water-absorbing and swelling elastic plugging agent in Embodiment 1 of the present invention.

[0026] Figure 3 This is a product image of the water-based drilling fluid water-absorbing and swelling elastic plugging agent in Embodiment 2 of the present invention. Detailed Implementation

[0027] The present invention will be further described in detail below with reference to embodiments, but the implementation of the present invention is not limited thereto.

[0028] Example 1 This embodiment provides a water-absorbing and swelling elastic plugging agent for water-based drilling fluid. The types and amounts of raw materials for the water-absorbing and swelling elastic plugging agent for water-based drilling fluid in this embodiment are shown in Table 1; the types and amounts of raw materials for the superabsorbent resin in this embodiment are shown in Table 2. Table 1. Types and dosages of raw materials for water-based drilling fluid water-absorbing and swelling elastic plugging agent in Example 1. Table 2. Types and amounts of raw materials for the superabsorbent resin in Example 1 In this embodiment, the superabsorbent resin is prepared through the following steps: S1. Add the water-absorbing monomer, water-locking monomer and initiator to distilled water in sequence, stir at room temperature until completely dissolved, and remove oxygen by bubbling with inert gas to obtain the reaction monomer solution. S2. The monomer solution in step S1 is stirred and reacted for 4-8 hours under the condition of inert gas bubbling to remove oxygen, and the reaction temperature is 40℃-70℃. After the reaction, the water is dried and the solution is ground to obtain a superabsorbent resin.

[0029] In this embodiment, a water-based drilling fluid water-absorbing and swelling elastic plugging agent is prepared through the following steps: S11. Add the polyolefin elastomer matrix material and the reinforcing matrix material to a high-speed mixer and stir at a speed of 1300 r / min to 1400 r / min, a temperature of 180℃ to 190℃, and a time of 2 min to 3 min. S12. After stirring, add the polyolefin elastomer matrix material crosslinking agent, reinforcing agent A, reinforcing agent B, superabsorbent resin, plasticizer, release agent and antioxidant in sequence. Stir at high speed, with a speed of 1300 r / min to 1400 r / min, a temperature of 180℃ to 190℃, and a time of 12 min to 15 min. S13. After mixing, sieve out particles with a diameter of 10 to 40 mesh; this is the water-based drilling fluid absorbent and expandable elastic plugging agent. Figure 2 The image shown is a product diagram of the water-based drilling fluid water-absorbing and swelling elastic plugging agent of this embodiment.

[0030] Example 2 The difference between this embodiment and Embodiment 1 is that, in this embodiment, the types and amounts of raw materials for the water-based drilling fluid absorbent and swellable elastic plugging agent are shown in Table 3; the types and amounts of raw materials for the superabsorbent resin are shown in Table 4; and the preparation methods for the superabsorbent resin and the water-based drilling fluid absorbent and swellable elastic plugging agent in this embodiment are the same as in Embodiment 1. Figure 3 The image shown is a product diagram of the water-based drilling fluid water-absorbing and swelling elastic plugging agent of this embodiment. Table 3. Types and dosages of raw materials for water-based drilling fluid water-absorbing and swelling elastic plugging agent in Example 2. Table 4. Types and amounts of raw materials for the superabsorbent resin in Example 2 Example 3 The difference between this embodiment and Embodiment 1 is that, in this embodiment, the types and amounts of raw materials for the water-based drilling fluid water-absorbing and swelling elastic plugging agent are shown in Table 5; the types and amounts of raw materials for the superabsorbent resin are shown in Table 6; and the preparation methods of the superabsorbent resin and the water-based drilling fluid water-absorbing and swelling elastic plugging agent in this embodiment are the same as in Embodiment 1.

[0031] Table 5. Types and dosages of raw materials for water-based drilling fluid water-absorbing and swelling elastic plugging agent in Example 3. Table 6. Types and amounts of raw materials for the superabsorbent resin in Example 3 Example 4 The difference between this embodiment and embodiment 1 is that, in this embodiment, the types and amounts of raw materials for the water-based drilling fluid water-absorbing and swelling elastic plugging agent are shown in Table 7; the types and amounts of raw materials for the superabsorbent resin are shown in Table 8; and the preparation methods of the superabsorbent resin and the water-based drilling fluid water-absorbing and swelling elastic plugging agent in this embodiment are the same as in embodiment 1.

[0032] Table 7. Types and dosages of raw materials for the water-based drilling fluid water-absorbing and swelling elastic plugging agent in Example 4. Table 8. Types and amounts of raw materials for the superabsorbent resin in Example 4 Example 5 The difference between this embodiment and Embodiment 1 is that, in this embodiment, the types and amounts of raw materials for the water-based drilling fluid water-absorbing and swelling elastic plugging agent are shown in Table 9; the types and amounts of raw materials for the superabsorbent resin are shown in Table 10; and the preparation methods of the superabsorbent resin and the water-based drilling fluid water-absorbing and swelling elastic plugging agent in this embodiment are the same as in Embodiment 1.

[0033] Table 9. Types and dosages of raw materials for the water-based drilling fluid water-absorbing and swelling elastic plugging agent in Example 5. Table 10. Types and amounts of raw materials for the superabsorbent resin in Example 5 Comparative Example 1 Compared with Example 1, no reinforcing matrix material was added in this comparative example. The types and amounts of raw materials for the water-based drilling fluid water-absorbing and swelling elastic plugging agent in this comparative example are shown in Table 11. The types and amounts of raw materials for the superabsorbent resin in this example are shown in Table 12. The preparation methods of the superabsorbent resin and the water-based drilling fluid water-absorbing and swelling elastic plugging agent in this comparative example are the same as those in Example 1.

[0034] Table 11. Types and dosages of raw materials for water-based drilling fluid water-absorbing and swelling elastic plugging agent in Comparative Example 1 Table 12. Types and amounts of raw materials used in the superabsorbent resin of Comparative Example 1 Comparative Example 2 Compared with Example 2, no superabsorbent polymer was added in this comparative example. The types and amounts of raw materials for the water-based drilling fluid water-absorbing and expanding elastic plugging agent in this comparative example are shown in Table 13. No superabsorbent polymer was added in this example.

[0035] Table 13. Raw material types and dosages of water-based drilling fluid water-absorbing and swelling elastic plugging agent in Comparative Example 2 Comparative Example 3 Compared with Example 3, no crosslinking agent was added in this comparative example. The types and amounts of raw materials for the water-based drilling fluid water-absorbing and swelling elastic plugging agent in this comparative example are shown in Table 14. The types and amounts of raw materials for the superabsorbent resin in this example are shown in Table 15. The preparation methods of the superabsorbent resin and the water-based drilling fluid water-absorbing and swelling elastic plugging agent in this comparative example are the same as those in Example 3.

[0036] Table 14. Raw material types and dosages of water-based drilling fluid water-absorbing and swelling elastic plugging agent in Comparative Example 3 Table 15. Types and amounts of raw materials used in the superabsorbent resin of Comparative Example 3 Comparative Example 4 Compared with Example 4, no plasticizer or release agent was added in this comparative example. The types and amounts of raw materials for the water-based drilling fluid water-absorbing and swelling elastic plugging agent in this comparative example are shown in Table 16. The types and amounts of raw materials for the superabsorbent resin in this example are shown in Table 17. The preparation methods of the superabsorbent resin and the water-based drilling fluid water-absorbing and swelling elastic plugging agent in this comparative example are the same as those in Example 4.

[0037] Table 16. Raw material types and dosages of water-based drilling fluid water-absorbing and swelling elastic plugging agent in Comparative Example 4 Table 17. Types and amounts of raw materials used in the superabsorbent resin of Comparative Example 4 Comparative Example 4 failed to prepare the material for the following reasons: SBS, polypropylene, and other polymeric materials typically have high viscosity and strong intermolecular forces. Without plasticizers, the materials have high hardness and rigidity, poor flowability, and easily adhere to the surface of processing equipment. Release agents, on the other hand, form a protective film between the metal surface of the processing equipment and the material, reducing the adhesion between them. Lacking these two additives, the polymeric material comes into close contact with the processing equipment during processing, and the intermolecular attraction causes the material to adhere firmly to the metal surface of the equipment, making it difficult to demold smoothly, thus leading to preparation failure.

[0038] Comparative Example 5 (Superabsorbent resin with only water-absorbing monomers and no water-locking monomers) Compared with Example 5, in this comparative example, only water-absorbing monomers were added to the superabsorbent resin, and no water-locking monomers were added. The types and amounts of raw materials for the water-based drilling fluid water-absorbing and swelling elastic plugging agent in this comparative example are shown in Table 18. In this example, the types and amounts of raw materials for the superabsorbent resin are shown in Table 19, and only water-absorbing monomers were added without water-locking monomers. The preparation methods of the superabsorbent resin and the water-based drilling fluid water-absorbing and swelling elastic plugging agent in this comparative example are the same as those in Example 5.

[0039] Table 18 shows the types and dosages of raw materials for the water-based drilling fluid water-absorbing and swelling elastic plugging agent used in Comparative Example 5. Table 19. Types and amounts of raw materials used in the superabsorbent resin of Comparative Example 5 Test case This test example tests the water-based drilling fluid water-absorbing and swelling elastic plugging agent prepared in Examples 1-5, including compressive modulus test and volume expansion rate test. The compressive modulus test was conducted as follows: the material was molded to obtain a cylindrical sample with a diameter and height of 10 mm. A 20 kg sensor was used during the test, and the compression rate was 2 mm / min. The compressive modulus was calculated from the slope of the compression curve. The experimental results are shown in Table 20. Table 20. Test results of compressive strength of the sealing agents provided in Examples 1-5 and Comparative Examples 1-5 of the present invention. Comparative Example 1, without a reinforcing matrix material, showed a decrease in the mechanical properties of the final product compared to Example 1. The reasons are as follows: SBS itself is a thermoplastic elastomer, and its molecular structure determines its relatively low strength. In contrast, PC, PS, and PP, as reinforcing matrix materials, possess higher mechanical strength. In blends of SBS and reinforcing matrix materials, the presence of the reinforcing matrix material enhances the overall mechanical properties. Secondly, SBS has a low glass transition temperature and is relatively soft at room temperature, making it prone to deformation. The rigid structure of the reinforcing matrix material in the blend, especially PS and PC, helps improve resistance to deformation.

[0040] Comparative Example 2, which does not contain superabsorbent resin, shows that the mechanical properties remain largely unchanged compared to Example 2, and the superabsorbent resin does not affect the mechanical strength of the material.

[0041] Comparative Example 3, without a crosslinking agent, showed reduced mechanical strength compared to Example 3. The crosslinking agent enables the formation of a crosslinked network structure between SBS molecular chains. Without the crosslinking agent, the SBS molecular chains are relatively independent and prone to relative sliding under external forces, resulting in weak resistance to deformation. However, with the addition of the crosslinking agent, the crosslinked structure restricts the movement of the molecular chains, improving the material's rigidity and modulus. This allows the blend to better maintain its shape under external forces, making it less prone to deformation and damage, thus exhibiting higher mechanical strength.

[0042] In Comparative Example 5, the superabsorbent resin contains only water-absorbing monomers. Compared with Example 5, the mechanical properties remain largely unchanged, and the structure of the superabsorbent resin does not affect the mechanical strength of the material.

[0043] As shown in Table 20, the compressive modulus of the plugging agents provided in Examples 1-5 of this invention is all greater than 5 MPa, indicating that they can effectively withstand formation pressure, seal leaking layers, and prevent leakage. The reasons are as follows: I. From the perspective of mechanical properties The compressive modulus reflects a material's resistance to deformation under pressure. A compressive modulus greater than 5 MPa indicates that the plugging agent possesses high stiffness and strength. After entering the leaky formation, facing formation pressure, the plugging agent can maintain its shape and structural integrity, preventing easy compression and deformation. This effectively fills the voids and cracks in the leaky formation, forming a robust sealing barrier. For example, in high-pressure formation environments, if the compressive modulus of the plugging agent is low, it will deform rapidly under pressure, failing to adhere tightly to the leaky formation wall, leading to sealing failure. However, when the compressive modulus is greater than 5 MPa, the plugging agent can withstand the pressure of the formation and maintain a stable sealing state.

[0044] II. Angle of Interaction with Strata Tight Adhesion: The high compressive modulus allows the plugging agent to generate sufficient contact pressure with the formation wall. When the plugging agent is pumped into the lost formation, it adheres tightly to the formation under pressure. Due to its high compressive modulus, the plugging agent is not easily pushed away by formation pressure, thus forming a stable sealing layer within the lost formation. This tight adhesion prevents drilling fluid from continuing to flow into the lost formation, achieving effective control of leakage. For example, in fractured lost formations, the plugging agent needs sufficient compressive strength to embed itself in the fracture and bond tightly to the wall, preventing drilling fluid from seeping out of the fracture.

[0045] Enhancing Formation Strength: The presence of plugging agents can enhance the overall strength of the formation surrounding the lost layer. When the compressive modulus is greater than 5 MPa, the plugging agent can not only withstand the formation pressure itself but also transfer some of the pressure to the surrounding formation, thereby improving the formation's bearing capacity. This enhancing effect helps stabilize the lost layer structure and prevent further leakage. For example, in loose formations, the high compressive modulus of the plugging agent can reinforce the formation and improve its resistance to pressure.

[0046] III. From the perspective of the stability of the leak sealing effect Long-term effectiveness: In formation environments, pressure can vary over time and during drilling operations. Poisoning agents with a compressive modulus greater than 5 MPa maintain stable performance under long-term pressure, resisting deformation or damage. This ensures the durability of the plugging effect and reduces the need for repeated plugging operations due to agent failure. For example, in long-term oil and gas wells, the plugging agent needs to withstand prolonged formation pressure; a high compressive modulus ensures effective sealing of the lost circulation zone throughout the entire production cycle.

[0047] Anti-interference capability: Various interference factors may be encountered during drilling, such as vibration and temperature changes. Poisoning agents with high compressive modulus have strong resistance to these interferences, maintaining their sealing performance unaffected. Even in complex downhole environments, they can stably withstand formation pressure and prevent leakage. For example, during drilling, drill string vibration may affect the poisoning agent. If the poisoning agent has a low compressive modulus, it may loosen or deform under vibration, thus reducing the sealing effect. Poisoning agents with high compressive modulus, however, can better resist such interference, ensuring the reliability of the sealing.

[0048] The volumetric expansion rate test is conducted as follows: A cylindrical sample with a diameter and height of 50 mm is obtained by molding the material. This sample is then added to a water-based drilling fluid and hot-rolled at 160°C for a period of time. The diameter and height are measured before and after expansion, and the volume is calculated to obtain the volumetric expansion rate at different times. The volumetric expansion rate is calculated using the following formula.

[0049] Where: V -- expansion rate, %; V0 -- initial volume, mL; V 1- Volume after expansion, mL.

[0050] The drilling fluid formula is as follows: 2% soil + 0.5% NaOH + 2% CMC-LV + 8% SMC + 5% SMP-I + 3% KCl + barite, with a density of 1.45 g / cm³. 3 .

[0051] The results of the 16-hour volume expansion rate experiment are shown in Table 21. The results of the volume expansion rate experiment at different times are shown in Table 21. Figure 1 .

[0052] Table 21. 16-hour volume expansion rate test results of the sealing agents provided in Examples 1-5 and Comparative Examples 1-5 of the present invention. From Table 21 and Figure 1 It can be seen that the volume expansion rate of the plugging agent provided in the embodiments of the present invention increases with time, and is greater than 90% after 16 hours, indicating that it has excellent water absorption and expansion effect. In actual use, it can absorb water in drilling fluid and expand to better seal the leaking layer.

[0053] Comparative Example 1, using unreinforced PP as the matrix material, showed a slightly higher volume expansion rate compared to Example 1. The reason is as follows: PP has a relatively regular molecular structure, which facilitates the close arrangement of molecular chains under certain conditions, forming crystalline regions. At an appropriate cooling rate, PP undergoes crystallization. Crystallization gives PP higher strength, hardness, and heat resistance. However, PP crystallization limits water absorption, so without PP, the volume expansion rate is even higher.

[0054] Comparative Example 2, without superabsorbent polymer (SAP), exhibited an extremely low volume expansion rate compared to Example 2. SAP can rapidly absorb large amounts of water, causing significant volume expansion of the material; without SAP, the material exhibited an extremely low volume expansion rate.

[0055] Comparative Example 3, without a crosslinking agent, showed a slightly higher volume expansion rate compared to Example 3. The crosslinking agent enables the SBS molecular chains to form a crosslinked network structure. Without the crosslinking agent, the SBS molecular chains are relatively independent and prone to relative movement. However, with the addition of the crosslinking agent, the crosslinked structure restricts the movement of the molecular chains and also limits the water absorption effect.

[0056] In Comparative Example 5, the superabsorbent resin contained only water-absorbing monomers. Compared with Example 5, the water absorption volume expansion rate was reduced because the sulfonic acid structure in the water-locking monomer had higher hydrophilicity and water absorption capacity than the amide and carboxylic acid structures in the water-absorbing monomers.

[0057] Application examples In this application example, a Type 71 fluid loss meter was used to evaluate the temperature resistance and plugging effect of the plugging agents in Examples 1-3. The experimental method is as follows: 400 mL of distilled water, 16.0 g of sodium bentonite for drilling fluid testing, and 0.64 g of anhydrous sodium carbonate were added to a high-speed stirring cup and stirred for 20 min with a high-speed stirrer. The stirring was interrupted twice to scrape off the adhering material on the container wall. The mixture was then sealed and cured for 24 h at 25℃±1℃ to obtain the base slurry. Different proportions of plugging agent were added to the base slurry to obtain the sample slurry. The base slurry and sample slurry were poured into the mud cup of the Type 71 fluid loss meter to the mark (without filter paper in the cup), and then placed in a heating mantle. The temperature was raised to 160℃ within 30 min. Connect the air supply device, keep the upper valve stem unobstructed, remove the lower valve stem (a small amount of mud will drip out from the bottom hole at this time), quickly place the measuring cylinder to collect the mud, turn on the air supply, slowly and evenly pressurize to 5MPa within 1 minute, stabilize the pressure for 30 minutes, collect and accurately read the volume of mud flowing out from the bottom hole, which is the amount of mud loss. Calculate the reduction rate R of the leakage using the following formula.

[0058] Where: R—reduction rate of slurry loss, %; M1—leakage of base slurry, mL; M—leakage of test slurry, mL. The test results are shown in Table 22.

[0059] Table 22 Test results of the temperature resistance and leak-stopping effect of the sealant provided in Examples 1-5 and Comparative Examples 1-5 of the present invention Comparative Examples 1 and 3 showed decreased mechanical properties compared to Examples 1 and 3, respectively, resulting in a reduced sealing effect. Low-strength sealing agents are unable to withstand pressure and fluid erosion when sealing leaks. When the sealing agent enters the simulated leakage channel, its insufficient strength makes it easily dispersed or deformed by subsequent fluid flow, failing to form an effective sealing barrier. Consequently, the leakage channel cannot be completely blocked, allowing fluid to continuously flow out, leading to a large leakage volume.

[0060] Comparative Examples 2 and 5 showed decreased mechanical properties compared to Examples 2 and 5, respectively, resulting in a reduced sealing effect. When the sealing agent exhibits volume expansion characteristics, leakage decreases. When the sealing agent enters the leakage channel, its volume expansion causes it to tightly fill the channel, increasing the contact pressure with the channel wall. This tight filling and pressure effectively prevents fluid from continuing to flow through the leakage channel. Simultaneously, the expanded sealing agent can better adapt to leakage channels of different shapes and sizes, improving the integrity of the seal. Furthermore, volume expansion enhances the stability of the sealing agent, making it less susceptible to being washed away by fluid, thus ensuring continued sealing and reducing leakage.

[0061] As shown in Table 22, the leakage reduction rate gradually increased with the increase of the amount of sealing agent in Examples 1-5, and the pressure resistance could reach 5 MPa, demonstrating excellent temperature resistance, pressure resistance and sealing effect, showing a good application prospect.

[0062] It is understood that the present invention has been described through some embodiments, and those skilled in the art will recognize that various changes or equivalent substitutions can be made to these features and embodiments without departing from the spirit and scope of the invention. Furthermore, under the teachings of the present invention, these features and embodiments can be modified to adapt to specific situations and materials without departing from the spirit and scope of the invention. Therefore, the present invention is not limited to the specific embodiments disclosed herein, and all embodiments falling within the scope of the claims of this application are within the protection scope of the present invention.

Claims

1. A water-based drilling fluid water-absorbing and swelling elastic plugging agent, characterized in that: Includes the following components in parts by weight: Polyolefin elastomer matrix material: 100 parts; Reinforced matrix material: 15-20 parts; Crosslinking agent for polyolefin elastomer matrix materials: 0.8 parts to 1.5 parts; Enhancer A: 8-15 parts; Enhancer B: 20-30 parts; Superabsorbent polymer: 15-30 parts; Plasticizer: 15-20 parts; Release agent: 0.2 parts to 0.8 parts; Anti-aging agent: 0.5 parts to 1 part.

2. The water-based drilling fluid water-absorbing and swelling elastic plugging agent according to claim 1, characterized in that: The superabsorbent resin is prepared by the following steps: S1. Add the water-absorbing monomer, water-locking monomer and initiator to distilled water in sequence, stir at room temperature until completely dissolved, and remove oxygen by bubbling with inert gas to obtain the reaction monomer solution. S2. The monomer solution in step S1 is stirred and reacted under anaerobic conditions for 4-8 hours at a reaction temperature of 40℃-70℃. After the reaction, the solution is dried and ground to obtain a superabsorbent resin.

3. The water-absorbing, swelling, elastic plugging agent for water-based drilling fluid according to claim 2, characterized in that: The absorbent monomer is one or more of sodium acrylate, sodium methacrylate, acrylamide, and methacrylamide.

4. The water-absorbing, swelling, elastic plugging agent for water-based drilling fluid according to claim 2, characterized in that: The water-locking monomer is one or more of sodium 2-acrylamide-2-methylpropanesulfonate, sodium p-styrenesulfonate, sodium propylenesulfonate, and sodium methpropylenesulfonate.

5. The water-absorbing, swelling, elastic plugging agent for water-based drilling fluid according to claim 2, characterized in that: The mass ratio of the water-absorbing monomer, the water-locking monomer, and the initiator is 0.2-0.3:0.7-0.8:0.005-0.01; the total concentration of the reaction monomer solution is 200g / L-300g / L.

6. The water-absorbing, swelling, elastic plugging agent for water-based drilling fluid according to claim 1, characterized in that: The polyolefin elastomer matrix material is styrene-butadiene-styrene block copolymer (SBS); the reinforcing matrix material is one or more of polypropylene, polystyrene, and polycarbonate.

7. The water-absorbing, swelling, elastic plugging agent for water-based drilling fluid according to claim 1, characterized in that: The reinforcing agent A is one or more of silica, carbon black, and calcium carbonate, and the particle size of reinforcing agent A is 25μm-50μm; the reinforcing agent B is carbon nanotubes, the length of which is 20μm-25μm, and the aspect ratio of which is 800:1-1000:

1.

8. The water-absorbing, swelling, elastic plugging agent for water-based drilling fluid according to claim 1, characterized in that: The plasticizer is one or more of paraffin oil, aromatic oil and naphthenic oil, and the crosslinking agent of the polyolefin elastomer matrix material is a peroxide crosslinking agent.

9. The water-absorbing, swelling, elastic plugging agent for water-based drilling fluid according to claim 1, characterized in that: The separating agent is one or more of zinc stearate, polyvinyl alcohol, and paraffin.

10. A method for preparing a water-based drilling fluid water-absorbing and swelling elastic plugging agent, characterized in that: The preparation method of the water-based drilling fluid water-absorbing and swelling elastic plugging agent according to any one of claims 1-10 includes the following steps: S11. Add the polyolefin elastomer matrix material and the reinforcing matrix material to a high-speed mixer and stir at a speed of 1300 r / min to 1400 r / min, a temperature of 180℃ to 190℃, and a time of 2 min to 3 min. S12. After stirring, add the polyolefin elastomer matrix material crosslinking agent, reinforcing agent A, reinforcing agent B, superabsorbent resin, plasticizer, release agent and antioxidant in sequence. Stir at high speed, with a speed of 1300 r / min to 1400 r / min, a temperature of 180℃ to 190℃, and a time of 12 min to 15 min. S13. After mixing, the particles with a particle size of 10 to 40 mesh are screened out, which is the water-based drilling fluid water-absorbing and expanding elastic plugging agent.

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